Of course they weren't. But, like lots of other good ideas, literacy tests could be abused.
In the day when minorities didn't have the same education opportunities as the majority, opposition to literacy tests was legitimate. Such opposition voiced today has no basis in fact, but is an emotional smokescreen for the left's agenda.
I believe the citizenship test given to immigrants would be a good one.
I'd bet a majority of voting Americans wouldn't be able to pass this test.
Personally, I think voting should be restricted to tax payers. I'm not delusional to think this will ever happen. The sad fact is that the class with their hands out will always vote themselves more entitlements and as this number grows, this will be the class that wins elections. Rome was finished when the citizens figured out they could vote themselves largess from the public treasury and like ancient Rome, the age of American greatness exists only in the history books.